This present invention relates generally to optical systems. More particularly, the invention relates to a method and structure for an optical micro-electromechanical systems (MEMS) including a flexible landing structure configured to support a reflective surface. Merely by way of example, the invention has been applied to the structure of a spatial light modulator with a high fill ratio and antistiction features. The method and device can be applied to spatial light modulators as well as other devices, for example, micro-electromechanical sensors, detectors, and displays.
Spatial light modulators (SLMs) have numerous applications in the areas of optical information processing, projection displays, video and graphics monitors, televisions, and electrophotographic printing. Reflective SLMs are devices that modulate incident light in a spatial pattern to reflect an image corresponding to an electrical or optical input. The incident light may be modulated in phase, intensity, polarization, or deflection direction. A reflective SLM is typically comprised of an area or two-dimensional array of addressable picture elements (pixels) capable of reflecting incident light.
Some conventional SLMs utilize array designs that include an array of micro-mirrors with a set of electrodes and a memory array positioned underneath each of the micro-mirrors. For display applications, the micro-mirrors are generally fabricated using semiconductor processing techniques to provide devices with dimensions on the order of 10 μm×10 μm. Using such small mirrors enables display applications to use SLMs in applications characterized by increased image resolution for a given display size. Merely by way of example, HDTV systems, with a resolution of 1,080 scan lines×1,920 pixels/line, are currently available to consumers.
One of the concerns related to the micro-mirrors used in reflective MEMS-based SLMs is stiction between the micro-mirrors and surfaces with which the micro-mirrors may come in contact. An example of such surfaces would be landing structures or other mechanical stops that support portions of the micro-mirror in an activated state. Surface forces acting between the micro-mirrors and the landing structures, for example, are sometimes referred to as “stiction” forces, since in some MEMS, parasitic forces arise from a combination of MEMS components sticking together and from friction, thus the term stiction. These parasitic forces may be strong enough to overcome the restoring force provided by spring-like elements of the MEMS, resulting in an undesirable adhesion of the micro-mirror to the landing structures.
Additionally, some optical MEMS designs utilize a solid structure, for example, a solid post, as a mechanical stop to arrest the rotation of the micro-mirror in an activated state. Repeated contact between the micro-mirror and such a solid landing structure may result in wear and tear at the contacting surfaces, degrading device performance and reliability over time. As an example, deterioration of surfaces at the contact region between the micro-mirrors and the landing structures may result in surface non-uniformity, thereby further increasing the stiction forces.
Adhesion of the micro-mirror to the landing structure will adversely impact long-term reliability of the optical MEMS. For example, failure of a single micro-mirror to release from the activated position may cause a pixel of the display to become permanently dark or bright, depending on the optical design. Thus, there is a need in the art for methods and systems to reduce stiction forces present in optical MEMS.